Sorry for the delay. I found my plans, hope they can be seen. I have found that BlueBirds & Tree Swallows will co-exist quite well if you alternate new houses between the existing houses. I suspect this means they sort of claim them every year. I also have had a sparrow problem solved very early with 22 shot shell ammo. You have to be courageous about killing the sparrows, they are survivors, too. Also, early on, we had a blow-fly problem requiring me to rebuild some nests while the hatchlings were stll very young. The parents will let you do this. I wound up inserting some wire mesh grid into the bottom of the cages with folds in the mesh to keep them about 1/2 inch above the bottom of the nest. I also sprayed insecticide on the bottom of the house before the scouts showed up. I often throw some fresh soft grass clippings on the ground in front of the house as an offering. You will find that Chickadees like the houses, too if near a pine tree. So what, I have plenty of houses for them. You call call they down with a "dee dee' call. Nothing feels so cool as to have them eat out of your hand. Very playfull, too, hanging upside down from your fingers to peck at the hair on your hand.